The invention relates to a measuring device for measuring a focused laser beam. The laser beam to be measured is employed, in particular, in the ophtalmic laser surgery, such as in a photorefractive treatment of the cornea or the lens. Of course, this is merely an example; principally, the invention is not subject to any limitations with respect to the application purpose of the laser beam to be measured. A precise knowledge of certain beam parameters is generally necessary for many laser applications, with only two out of numerous other examples besides the laser surgery of the eye, the photolithography in the semi-conductor technology as well as the laser scanning or laser writing of optical data carriers being mentioned herein.
Beam parameters of interest of a laser beam often include the beam diameter, in particular in the area of the beam waist, as well as the beam divergence, but other parameters, too, such as the diffraction index (usually expressed as M2) or the intensity profile transverse to the beam direction.
For the measurement of a laser beam so-called knife edge or slit methods are known, in which a blade or a sufficiently narrow slit is moved transversely through the beam and transmitted power is measured depending on the blade or slit position, respectively, by means of a detector. By the differentiation of the transmission curve which has been obtained in this manner, the intensity profile may subsequently be determined, by means of which in turn the beam diameter may be determined.
As an alternative to the above transmission measuring methods which are based on “scanning” of the beam, it is known, e.g. from U.S. Pat. No. 4,917,489, to magnify the laser beam by means of a single magnification lens and to direct the magnified laser beam following a suitable intensity attenuation to an image pickup device (image sensor). It is then possible to calculate the beam diameter at the object-side lens focus under consideration of the magnification factor of the lens from the generated image of the laser beam.
In contrast, an inventive measuring device for the measurement of a focused laser beam comprises a magnification lens system with at least two lenses disposed in series in the beam path of the laser beam, wherein each pair of successive lenses of the magnification lens system has coinciding focal points, an electronic image sensor disposed behind the magnification lens system at a focal point thereof, for capturing an image of the magnified laser beam, an adapter which encloses the beam path, for coupling the measuring device to a laser system which provides the laser beam, with the adapter forming an abutment surface for the laser system, which abutment surface is axially directed with respect to a beam axis of the laser beam, as well as longitudinal adjustment means which permit a simultaneous adjustment of the lenses of the magnification lens system and the image sensor along the beam path with respect to a reference point of the measuring device provided on the adapter.